The present invention is related to the techniques for the elimination of pollutants, and more particularly, it is related to a combined system for the elimination of pollutants from gaseous effluents.
Pollution has existed since man began to modify his environment by using tools, managing fire, and performing agriculture, thus differentiating himself from other predators. For instance, the arrival of agriculture gave place to alterations in the existing ecosystems. However, it was in a very similar way to what happened in natural phenomena.
Although such changes in the environment surrounding man are very ancient, it was until the industrial revolution when man obtained enough control over the environment as to deteriorate it. Even though such deterioration is relatively recent with respect to human history, there had to pass almost two hundred years before solutions started to be sought. In view of this, the new challenge that civilization has to face nowadays consists of knowing how to make maximum the availability of necessary goods as the cost in terms of pollution, use of natural resources and other related issues is minimized.
Other of the most affected resources, mainly in big cities, is air, which is polluted with all kind of gases and floating particles. Against what could be thought, molecules of inorganic nature are the most common pollutants in atmosphere, except for partially burnt hydrocarbons and other substances coming regularly from combustion processes. For example, in the treatment of metallic sulfur minerals, the toasting processes can be an important pollution source if there is no effort to catch the sulfur dioxide that is discharged as byproduct.
A classical example of this problem is described in the article of C. R. Hursh in 1935 in the brochure: xe2x80x9cLocal Climate of Cooper Basin of Tenessee as Modified by Removal of Vegetationxe2x80x9d, USDA, number 774. There, it is described what happened in Copperhill, Tenn., where the products of metallic sulfur minerals toasting have altered the woods in an area of almost 220 km2. The woods have disappeared almost completely, although some zones with grass in a girdle covering approximately 7000 hectares still exist, thus leaving a remaining area of 28000 hectares completely without vegetation.
Less known is the damage caused by a zinc foundry in Leigh gap, Pa. It is presented in the article of M. J. Jordan in 1975 in the magazine xe2x80x9cEcologyxe2x80x9d, number 56, volume 78. The damage was caused by emissions of sulfur dioxide, zinc, cadmium, copper and lead. The samples of the ground, taken approximately two kilometers away from the foundry, contained more than 8% of zinc.
As it can be seen from the latter, air pollutants can also produce pollution of the ground and ecosystems due to the fact that they travel easily and rapidly. Air pollutants can be classified in different ways, considering both the emitting source and the physical and chemical features of the emissions.
It is quite difficult to characterize the pollution producing sources. There has been estimated that in the United States 60% of the air pollution comes from engine driven vehicles and 14% comes from electricity generating plants, as industry produces about 17%, the remaining 9% coming from air conditioning. The annual emission of pollutants in the United states is very meaningful since, as mentioned, engine driven vehicles contribute with about 60% of the total pollution, from which almost all is carbon monoxide, two thirds of hydrocarbons, one half of nitrogenous oxide and little fractions of other compounds.
The pollution due to combustion engine driven vehicles is a much bigger problem in big cities, and even more in the largest such as Mexico City. In big cities the extent of urban areas and the intense economic and social life forces people to travel great distances in order to perform their ordinary activities.
It is estimated that in Mexico City, vehicle emissions represent about 76% from the total pollutants emitted to the atmosphere; private vehicles emit more than half the pollutants of vehicular origin, and when using gasoline, they also produce lead oxides, sulfur and suspended particles.
Nevertheless, it is necessary to consider that pollutants come from fixed sources as well as from mobile sources. In developing countries it has been found that environmental pollution comes mainly from industries that throw their wastes illegally during the night, i.e., pollution comes from fixed sources.
On the other hand, in its simplest form, control of air pollution needs basic knowledge for establishing adequate criteria in order to maintain the freshness of air; ability to relate air quality to emission levels; establishment of emission limits or other control standards; means for measuring emissions and air quality and availability of practical techniques for reducing the emissions that pollute it.
In regard to the practical techniques for reducing emanations, even though it has been given attention to process changes that reduce polluting emissions, a great confidence has been given also to physical processes for eliminating such pollutants therefrom.
Within the existing techniques, a distinction is made between those developed for appliance on mobile sources directly and those developed to be used in fixed sources. It is worth mentioning that most of them have focussed on the treatment and control of emissions coming from fixed sources. This is probably due to the easiness of installation, operation and maintenance and to the pressure exerted by governments over industries, thus forcing them to install apparatus that enable them to comply with the increasingly strict rules in regard to the pollutants emitted to the atmosphere.
The apparatus used to clean the air from particles coming from fixed sources are based basically on aerodynamic catch, such as inertial impact, direct interception and diffusion. However, some apparatus use electrical and thermal forces, chemical reactions, and apply principles such as absorption, adsorption, condensation, etc.
Filtration is one of the most used methods, in which various types of filters are incorporated in direct interception processes as well as in diffusion processes, in a way that there can be achieved very high efficiencies not only with big particles but with the small ones. The use of these principles has resulted in the development of various technologies. For instance, Mexican Patent No. 131020 is related to an air purifying apparatus. It comprises at least one particle-filtering module in one of its walls and an activated carbon filter module, wherein the particle-filtering module comprises a filter for fine particles and one for bulky particles.
Another example is the portable air purifier of Mexican Patent Number 188350 which comprises one chamber with an air intake and an air outlet, as well as a filtration means provided inside the chamber between the air intake and the air outlet. They are assembled in such a way that when air crosses through the chamber, the particles are retained due to the filtration means.
Among the possible variations there can be found bag filters, which are capable of managing particles having diameters of less than 1 micron. However, they show the disadvantage of having a maximum operating temperature of 500xc2x0 F. and generating pressure drops higher than 4 in H2O, although they can achieve efficiencies around 99% and need little space for its operation. An additional inconvenient of these filters is the great sensitivity of the bags to humidity, filtration rates and temperature.
Obviously, there can be used different types of filters to achieve a better separation of the pollutants, as described in Mexican Patent Application number 9101571. The method is based on a filtration system comprising pre-filters, absolute filters and activated carbon filters that purify and sterilize polluted air, which is forced to pass through the same by means of one or more fans; thus achieving a retention efficiency of the filters of about 95%.
There have been made some efforts in order to achieve better results in collection by electrically charging the particles to be eliminated. These filters operate with a collecting efficiency of about 99.9%. This can be seen in the electrostatic filter air purifier shown in Mexican Patent Application No. 9501387, which comprises an electrode and an electrostatic filter that enhance separation and collection on pollutant emissions.
Another widely used technique is damp collectors that separate particles and operate due to the contact between particles contained in a gas stream with a liquid. Damp collectors generally use water, in the form of little drops, which is put in contact with the pollutants of the gas stream; the separation is due to the collision between the particles suspended in the gas stream and the little drops of water. Among damp collectors there can be found mainly spray towers, which can achieve efficiencies around 80%. Examples of use of these techniques can be found in the Mexican Patent Applications Nos. 9603017, 9600105 and 9301564.
Electrostatic precipitation is the most important technique in particle separation. In general terms, the particles present in a gas stream are electrically charged by means of a high voltage discharge coming from an electrode and are collected in collecting plates having an inverse polarity. Electrostatic precipitators can achieve efficiencies of 99% at optimal conditions, but its performance is still low under non-favorable conditions. Electrostatic precipitators are capable of retaining particles having diameters of less than 1 micron, operating within a temperature range between 40 and 850xc2x0 F. Electrostatic precipitators generally have pressure drops of less than 1 in H2O and operate with efficiencies close to 99%.
There can be considered as principal components of electrostatic precipitators the electrical discharge plate and the particle-collecting surface. Charging the particles with a high voltage, whether positively or negatively, produces the separation, and then let the charged particle to be attracted by the collecting surface, which has an opposite charge than the particle.
Within the existing electrostatic filtering apparatus are found those described in U.S. Pat. Nos. 3,967,939, 4,140,498, 4,194,888, 4,202,674, 4,626,262, 4,675,029, 5,039,318, 5,050,377, 5,121,601, 5,147,423, 5,248,324, 5,302,190 Y 5,439,508, among others.
Under the same principle, there are known apparatus operated by means of changes in the resistance as a method for the retention and separation of particles, which is found in U.S. Pat. No. 4,779,207, as U.S. Pat. Nos. 5,039.313 and 5,704,955 make use of conventional filters for the retention of such pollutants. Another similar method is the electrodynamic separation as described in U.S. Pat. No. 3,973,932.
Is worth mentioning, however, that filters in general are only used for eliminating suspended particles and not for eliminating other kinds of pollutants, such as gaseous type pollutants, for example.
On the other hand, condensation and precipitation principles are also useful methods for the separation of polluting emissions. As an example of the latter it is possible to mention Mexican Patents Nos. 186045 and 188200. They refer to processes for eliminating emissions by condensing and precipitating that comprise collecting the moisture charged air stream containing the emissions, of oil in this case, to be separated; cooling the moisture charged air that contains the emissions, which is collected at a moist saturation temperature at which the moisture contained in the air is condensed so as to form a liquid in such a way that an aqueous condensed liquid stream is formed and an outlet air stream containing moisture saturated air and liquid droplets; eliminating from the air stream the liquid droplets of the emissions in order to form a second condensed liquid stream containing an important part of the oil emissions; and heating the outlet air stream at a temperature over its moist saturation temperature in order to eliminate the humidity from the air and obtain an outlet air stream that can be discharged to the atmosphere. However, in this method is required the pollutant to be easily condensed, otherwise it would be maintained as gas and could not be eliminated by this method.
In general terms, most of the current techniques for treating gaseous polluted effluents of high efficiency present the inconvenience of requiring a liquid for the treatment, which in turn has to be post-treated to avoid pollution of effluents and ground. Additionally, the use of liquids generates corrosion in the apparatus and can be very sensitive to changes in particle properties thus decreasing its efficiency; and in general, they can only be used for certain kinds of pollutants. On the other hand, the apparatus that need not an additional fluid present low efficiency.
Nowadays, there are some apparatus capable to manage various types of 35 polluting emissions, both coming from fixed sources and from mobile sources. This ability is determined by the arrangement of its components and by the use of several of theabove-described techniques together. For instance, Mexican Patent No 180969 refers to an apparatus for separating environment-polluting agents. It is characterized by comprising a series of consecutive chambers that separate and retain polluting particles; a first chamber for the air reception which is provided with horizontal grilles with its openings covered with pre-filters that are maintained humid by means of a system of water spraying tubes; a second chamber that directs air and avoids the generation of turbulence; a third chamber comprising a plurality of deposit trays previously bath in a solution that enables it to retain such solid particles, as well as a steel mesh covered with filtrating means in order to trap the solid particles that were not retained by the mentioned trays; and a fourth chamber receiving the clean air coming from the third chamber to discharge it outside as a siphon.
From the above it can be observed that is possible to use some apparatus in a combined form and which combination results in a decrease of various types of pollutants present in a gas stream. Therefore, it is possible to use in the same method filters, pre-filters, washing techniques, precipitation, reaction, etc.
In Mexican Patent Application No 9603012 the improvements made to the last described apparatus are referred to, which consist of including a plurality of electrodes that allow the molecular breaking of the pollutants, which leads to a more efficient operation of the apparatus. Such electrodes perform an electronic bombardment on the effluent; thus generating ionization due to said electronic bombardment. Due to this reason this technique is also known as ionization. Actually, ionization by itself is used in air purifying apparatus. However, the efficiency of these apparatus is rather low and they are barely used for industrial gaseous effluent treatment.
Now then, in regard to mobile sources such as the combustion gases of automobiles, the most used apparatus are those of the catalytic type, which in addition to be expensive due to the noble metal content, they tend to be easily poisoned, thus decreasing its efficiency in a great extent.
In the specific case of engine combustion gases, although it has been achieved a decrease in the quantity of nitrous oxides, hydrocarbons, sulfur compounds and other polluting gases, the acid pH of the water expelled from the vehicle gas escapes has not been decreased. It is known that such water has pH values of approximately 4, this value being a very acid one for water. As it is easy to suppose, this phenomenon does not favor the elimination of acid rain nor of its harmful effects on health.
Consequently, for long it has been sought to overcome the inconveniences of prior art techniques for eliminating pollutant from gaseous streams by means of a combined system for the elimination of pollutants from gaseous effluents that allows to eliminate suspended particles such as gas pollutants, mainly coming from a combustion, without needing additional fluids for the treatment, which in addition has a high efficiency of pollutants removal.
Having in mind the drawbacks of the prior art, it is an object of the present invention to provide a combined system for the elimination of pollutants from gaseous effluents of easy and economic construction but with high efficiency and reliability for retaining in a great extent diverse solid pollutant particles suspended in air.
Another object of the present invention is to provide a combined system for the elimination of pollutants from gaseous effluents able to operate satisfactorily at extreme environmental conditions without presenting any changes or considerable variations regarding its efficiency. An additional object of the present invention is to provide a combined system for the elimination of pollutants from gaseous effluents that by means of a rapid and easy operation allows the maintenance and/or interchange of its internal parts.
It is also another object of the present invention to provide a combined system for the elimination of pollutants from gaseous effluents resulting to be very flexible in its manufacturing from a great variety of materials and shapes according to specific requirements.
Likewise, it is another object of the present invention to provide a combined system for the elimination of pollutants from gaseous effluents that allows to reduce the organic compounds expelled to the atmosphere, specially lower hydrocarbon chains.
Another object of the present invention is to provide a combined system for the elimination of pollutants from gaseous effluents that makes disappear the visible polluting particles that can be found suspended in the atmosphere.
Additionally, it is an object of the present invention to provide a combined system for the elimination of pollutants from gaseous effluents that allows to diminish the temperature of the gases expelled to the atmosphere.
It is also an object of the present invention to provide a combined system for the elimination of pollutants from gaseous effluents that allows a decrease of acidity in pluvial water as well as in the condensed water of the gas outlets of combustion engines.
Another object of the present invention is to provide a combined system for the elimination of pollutants from gaseous effluents that allows a decrease in the physical annoyances of people, generated by the exposure to atmospheres having high pollutant concentration.
In addition, another object of the present invention is to provide a combined system for the elimination of pollutants from gaseous effluents that can be used in both mobile sources and fixed sources. Still another object of the present invention is to provide a combined system for the elimination of pollutants from gaseous effluents that can be used in modular form.
It is also another object of the present invention to provide a combined system for the elimination of pollutants from gaseous effluents with a high particle retention level, specially for those toxic particles suspended in the environment. Another object of the present invention is to provide a combined system for the elimination of pollutants from gaseous effluents that allows a reduction in the amount of pollutant precursors expelled to the atmosphere.
It is an additional object of the present invention to provide a combined system for the elimination of pollutants from gaseous effluents that requires very low energy consumption for its operation. An additional object of the present invention is to provide a combined system for the elimination of pollutants from gaseous effluents that do not require additional fluids for the treatment but still having a high efficiency in pollutants removal.
A further object of the present invention is to provide an apparatus incorporating the combined system for the elimination of pollutants from gaseous effluents mentioned above.